The present invention relates to an improved method for preparing a mill quality, high solids, aqueous, carbonless CF coating that can be applied onto paper with very little drying. The coated paper is dimensionally stable and exhibits no, or very little, curl or cockle.
Carbonless paper is now widely used in the forms industry. A typical carbonless form is made up of one sheet, known as a CB sheet, which is the first page of the form and a second sheet, known as a CF sheet, which is the back page of the form. Where a form having more than two sheets is desired, as in the case where more than one copy is required, one or more sheets known as CFB sheets may be placed between the CF and the CB sheet. A CB sheet consists of a sheet of paper having a layer of microcapsules containing a color former coated on its back side, hence the designation CB or "coated back." A CF sheet consists of a sheet of paper carrying a layer of a developer material on its front side or "coated front" which reacts with the color former to produce a colored mark. A CFB sheet is coated on its front and back sides. The front is coated with developer and the back is coated with microcapsules. The manifold carbonless forms will usually comprise from about 2 to about 10 individual sheets and preferably from about 2 to about 4 individual sheets per form.
Generally speaking, two approaches have been taken to the manufacture of carbonless manifoldforms. In one approach the forms paper is coated at a paper mill and shipped to the forms manufacturer who prints, perforates and collates the form. In the second approach, the CF and CB coating compositions are applied to the form by the forms manufacturer on the forms press. The latter methods are herein referred to as "on press" methods as contrasted with "off press" methods where the CF and CB coatings are applied at the paper mill. One type of CF coating is a resin dissolved in an oil. The coating does not dry after application and a blurring appearance occurs in the CFB forms produced. Other coating methods employ a volatile organic solvent to dissolve the CF resin. Environmentally and economically, a water based coating is desirable.
A number of CF and CB coating compositions have been designed for application on the press. However, there are currently no aqueous print-on CF coatings of good quality available.
U.S. Pat. No. 4,186,115 describes a CB coating comprising a color precursor and a liquid radiation curable composition which cures to a frangible resin.
U.S. Pat. No. 4,091,122 discloses CF and CB coating compositions containing a color developer or color precursor and a liquid radiation curable substance.
U.S. Pat. No. 4,143,890 discloses a hot melt CB coating composition prepared by dispersing an encapsulated color precursor into a wax based composition.
U.S. Pat. Nos. 4,097,619 and 4,112,138 describe on press processes using the aforementioned hot melt and radiation curable CF and CB coating compositions.
U.S. Pat. No. 3,914,511 to Vassiliades discloses a process for spot printing aqueous-based CF and CB coating compositions using a printing roll having a raised resilient surface. According to the patent, the technique can be used to apply localized CB coating as well as CF coatings. The CF coatings are dispersions of acid clays, talc and other inorganic developers in water.
One of the drawbacks of prior on press aqueous CB and CF coating compositions is that they generally do not provide the image and/or typewriter intensity that off press coatings provide. One reason for this is that on press coating compositions are designed to set with little or no drying. This usually means that the coatings must be applied at lower coat weights than those applied at the mill which is generally in the range of about 3.3 pounds/1300 sq. in. As a consequence printing quality often suffers. In order to provide a sufficient quantity of developer material on the surface of the form to give high image density, high coat weights of these developer compositions are required. This has relegated the use of the aqueous resin dispersion to mill operations where drying capacity is available to set these high coat weights as opposed to on the press where the drying capacity is limited.